The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services. Therefore, efforts have been directed to developing High Speed Downlink Packet Access (HSDPA) for the purpose of providing a maximum data rate of 10 Mbps and to improve the radio capacity in the downlink. HSDPA achieves higher data speeds by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following briefly described below: shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
In shared channel transmission, radio resources, like spreading codes and transmission power in the case of Code Division Multiple Access (CDMA)-based transmission, are shared between users using time multiplexing. A high speed-downlink shared channel is one example of shared channel transmission. One significant benefit of shared channel transmission is more efficient utilization of available code resources as compared to dedicated channels. Higher data rates may also be attained using higher order modulation, which is more bandwidth efficient than lower order modulation, when channel conditions are favorable.
Radio channel conditions experienced on different communication links typically vary significantly, both in time and between different positions in the cell. In traditional CDMA systems, power control compensates for differences in variations in instantaneous radio channel conditions. With this type of power control, a larger part of the total available cell power may be allocated to communication links with bad channel conditions to ensure quality of service to all communication links. But radio resources are more efficiently utilized when allocated to communication links with good channel conditions. For services that do not require a specific data rate, such as many best effort services, rate control or adjustment can be used to ensure there is sufficient energy received per information bit for all communication links as an alternative to power control. By adjusting the channel coding rate and/or adjusting the modulation scheme, the data rate can be adjusted to compensate for variations and differences in instantaneous channel conditions.
For maximum cell throughput, radio resources may be scheduled to the communication link having the best instantaneous channel condition. Rapid channel dependent scheduling performed at the bases station allows for very high data rates at each scheduling instance and thus maximizes overall system throughput. Hybrid ARQ with soft combining increases the effective received signal-to-interference ratio for each transmission and thus increases the probability for correct decoding of retransmissions compared to conventional ARQ. Greater efficiency in ARQ increases the effective throughput over a shared channel.
FIG. 1 illustrates a high speed shared channel concept where multiple users 1, 2, and 3 provide data to a high speed channel (HSC) controller that functions as a high speed scheduler by multiplexing user information for transmission over the entire HS-DSCH bandwidth in time-multiplexed intervals. For example, during the first time interval shown in FIG. 1, user 3 transmits over the HS-DSCH and may use all of the bandwidth allotted to the HS-DSCH. During the next time interval, user 1 transmits over the HS-DSCH, the next time interval user 2 transmits, the next time interval user 1 transmits, etc.
High-speed data transmission is achieved by allocating a significant number of spreading codes (i.e., radio resources in CDMA systems) to the HS-DSCH. FIG. 2 illustrates an example code tree with a fixed Spreading Factor (SF) of sixteen. A subset those sixteen codes, e.g., twelve, is allocated to the high-speed shared channel. The remaining spreading codes, e.g., four are shown in the figure, are used for other radio channels like dedicated, common, and broadcast channels.
Although not necessarily preferred, it is also possible to use code multiplexing along with time multiplexing. Code multiplexing may be useful, for example, in low volume transmission situations. FIG. 3 illustrates allocating multiple spreading codes to users 1, 2, and 3 in code and time multiplexed fashion. During transmission time interval (TTI) 1, user 1 employs twelve codes. During transmission time interval 2, user 2 employs twelve spreading codes. However, in transmission time interval 3, user 1 uses two of the codes, and user 3 uses the remaining ten codes. The same code distribution occurs in TTI=4. In TTI=5, user 3 uses two of the codes while user 2 uses the remaining codes.
When the high speed downlink shared channel concept was initially conceived it was in response to the perception that most high data rate applications for 3G mobile terminals would be in the downlink direction, e.g., receiving web pages from the Internet at the mobile terminal, in response to low rate uplink web browser requests from the mobile terminal. The mobile user would likely not subscribe to such a service if the information required long time periods to download using normal data rates. By giving the mobile user a lot of bandwidth for short times when needed, e.g., to download a web page, that mobile user experiences a service approaching that which might be delivered over some fixed wire environments. This kind of asymmetry works well with certain services like web page browsing. But it is less satisfactory for more balanced services, e.g., where a large email is received and forwarded. And some services are particularly demanding in the uplink such as multimedia, interactive gaming, video conferencing, etc.
Thus, it would be desirable to provide a mobile terminal, where possible, the option of transmitting at a higher data rate in the uplink over an uplink channel, e.g., an “enhanced” uplink channel, if that mobile receives or can receive information in the downlink from the network at a high data rate over a high speed downlink channel. Indeed, the mobile user, even though largely unaware of current system load constraints and radio channel conditions, may very much desire and even demand the same or at least similar data transmission rates in both the downlink and the uplink. For example, if a mobile terminal user downloads a graphics file at a fast rate, that user might well expect to be able to send the same graphics file to another person in the uplink at about that same fast rate. Voice-over-IP and interactive gaming are other examples where a high speed data transmission rate for both uplink and downlink is desired. But at the same time, radio resources are limited, so it is not feasible to allow all mobile terminals to transmit at high data rates.
A mobile communications network supports mobile radio communications using radio channels associated with a cell including a high speed downlink shared radio channel for transmitting information from the mobile communications network to mobile terminals and uplink channels for transmitting information from the mobile terminals to the mobile communications network. A radio connection is established between a first mobile terminal receiving information from the mobile communications network over the high speed-downlink shared channel and transmitting information to the mobile communications network over a first uplink channel. A first downlink channel quality associated with a first data transmission of information over the high speed downlink shared radio channel to the first mobile terminal is determined. In a one example, the first downlink channel quality is determined based on information provided by the first mobile terminal. A first uplink data transmission rate limit is then set for information to be transmitted over the first uplink channel by the first mobile terminal based on the first downlink channel quality.
A second downlink channel quality associated with a second data transmission of information over the high speed downlink shared radio channel to a second one of the mobile terminals may also be determined. A second uplink data transmission rate limit for information to be transmitted over a second uplink channel by the second mobile terminal is also determined based on the second downlink channel quality. Assuming that the first downlink channel quality exceeds the second downlink channel quality, the first uplink data transmission rate limit is set greater than the second uplink data transmission rate limit. The first uplink data transmission rate limit is sent to the first mobile terminal, and the second uplink data transmission rate limit is sent to the second mobile terminal.
In one example situation, the first uplink data transmission rate limit correlates with a downlink data transmission rate to the first mobile terminal over the high speed downlink shared radio channel, which may be useful for balanced data communications applications. But the uplink transmission rate limit is not necessarily limited by the actual downlink transmission rate. Moreover, a load associated with the first uplink channel may be determined and also used in the process of determining the first uplink data transmission rate limit. In one example implementation, the first uplink data transmission rate limit is a function of the first downlink channel quality, the load, and a number of mobile terminals transmitting in uplink to the mobile communications network. The first uplink data transmission rate limit may also be a function of one or more additional parameters, e.g., a number of users transmitting.